对通用字符串对象进行编码会得到nil Swift

想一想绳子会是什么 "hello" 编码为JSON,看起来像。它看起来就像:

"hello"

不是吗?

这不是一个有效的JSON(根据 here )! 不能将字符串直接编码为JSON,也不能直接解码字符串。

例如,这个代码

let string = try! JSONDecoder().decode(String.self, from: "\"hello\"".data(using: .utf8)!)

将产生错误

JSON文本没有以数组或对象开头,并且没有设置允许片段的选项。

和

let data = try! JSONEncoder().encode("Hello")

将产生错误:

顶级字符串编码为字符串JSON片段。

这里的工作就是用专用的 set 方法由 UserDefaults 。您仍然可以使用泛型方法,但只需检查类型和强制转换:

if let str = object as? String {
    UserDefaults.standard.set(str, forKey: key)
} else if let int = object as? Int {
    ...

虽然Sweeper的评论很有帮助,应该是答案(因为没有他的回答,我无法得出自己的答案),但我仍然会继续分享我对Defaults类所做的事情,让它处理非JSON编码对象(例如String、Int、Array等等)。

这是:

默认值。敏捷的

import Foundation

enum MVDefaultsKey: String {
    case requestToken = "defaultsRequestToken"
    case someOtherKey = "defaultsKeyForTests"
}

/// The class that has multiple class functions for handling defaults.
/// Also has the helper class functions for handling auth tokens.
class MVDefaults {

    // MARK: - Functions

    /// Stores object.
    class func store<T: Encodable>(_ object: T, key: MVDefaultsKey) {
        let encoder = JSONEncoder()
        let encoded = try? encoder.encode(object)

        if encoded == nil {
            UserDefaults.standard.set(object, forKey: key.rawValue)
            return
        }

        UserDefaults.standard.set(encoded, forKey: key.rawValue)
    }

    /// Removes the stored object
    class func removeDefaultsWithKey(_ key: MVDefaultsKey) {
        UserDefaults.standard.removeObject(forKey: key.rawValue)
    }

    /// Returns stored object (optional) if any.
    class func getObjectWithKey<T: Decodable>(_ key: MVDefaultsKey, type: T.Type) -> T? {
        if let savedData = UserDefaults.standard.data(forKey: key.rawValue) {
            let object = try? JSONDecoder().decode(type, from: savedData)
            return object
        }

        return UserDefaults.standard.object(forKey: key.rawValue) as? T
    }
}

下面是我为测试默认方法而编写的测试(规范)。都过去了!

@testable import Movieee
import Foundation
import Quick
import Nimble

class MVDefaultsSpec: QuickSpec {
    override func spec() {
        describe("Tests for MVDefaults") {

            context("Tests the whole MVDefaults.") {

                it("tests the store and retrieve function for any Codable object") {

                    let data = stubbedResponse("MovieResult")
                    expect(data).notTo(beNil())
                    let newMovieResult = try? JSONDecoder().decode(MovieResult.self, from: data!)

                    MVDefaults.store(newMovieResult, key: .someOtherKey)

                    let retrievedObject = MVDefaults.getObjectWithKey(.someOtherKey, type: MovieResult.self)

                    // Assert
                    expect(retrievedObject).notTo(beNil())

                    // Assert
                    expect(retrievedObject?.movies?.first?.id).to(equal(newMovieResult?.movies?.first?.id))
                }

                it("tests the store and retrieve function for String") {

                    let string = "Ich bin ein Berliner"

                    MVDefaults.store(string, key: .someOtherKey)

                    let retrievedObject = MVDefaults.getObjectWithKey(.someOtherKey, type: String.self)

                    // Assert
                    expect(retrievedObject).notTo(beNil())

                    // Assert
                    expect(retrievedObject).to(equal(string))
                }

                it("tests the removal function") {

                    MVDefaults.removeDefaultsWithKey(.someOtherKey)

                    let anyRetrievedObject = UserDefaults.standard.object(forKey: MVDefaultsKey.someOtherKey.rawValue)
                    let stringRetrievedObject = MVDefaults.getObjectWithKey(.someOtherKey, type: String.self)

                    // Assert
                    expect(anyRetrievedObject).to(beNil())

                    // Assert
                    expect(stringRetrievedObject).to(beNil())
                }

                it("tests the store and retrieve function for Bool") {

                    let someBool: Bool = true

                    MVDefaults.store(someBool, key: .someOtherKey)

                    let retrievedObject = MVDefaults.getObjectWithKey(.someOtherKey, type: Bool.self)

                    // Assert
                    expect(retrievedObject).to(equal(someBool))

                    // Assert
                    expect(retrievedObject).notTo(beNil())
                }
            }
        }
    }
}